Method and device for assisting a driver of a vehicle

ABSTRACT

The invention relates to a method and a device for assisting a driver of a vehicle, said vehicle having an engine and a braking system, an accelerator that conveys the driver&#39;s wishes concerning acceleration to the engine, and a brake pedal that conveys the driver&#39;s wishes concerneing retardation to the braking system. In accordance with the method a speed profile is determined for the driving distance, which speed profile comprises a relation between a speed set point and position. Furthermore, the engine and the braking system are controlled on the basis of the speed profile and at least one actuator influences the accelerator or braking pedal of the vehicle in accordance with said control. The driver is permitted to override the influence of the actuator only if a force that is greater than a predetermined threshold value is applied on one of the pedals.

This application is the national phase under 35 U.S.C. §371 of PCTInternational Application No. PCT/SE00/01637 which has an internationalfiling date of Aug. 25, 2000, which designated the United States ofAmerica.

TECHNICAL FIELD

The present invention relates to a method and a device for assisting adriver of a vehicle, said vehicle having an engine and a braking system,an accelerator that conveys the driver's wishes concerning accelerationto the engine, and a brake pedal that conveys the driver's wishesconcerning retardation to the braking system.

The method in accordance with the invention comprises the steps of,taking into consideration several factors, such as a division of aspecific driving distance into shorter segments, determining a speedprofile for the driving distance, which speed profile comprises arelation between a speed set point and position, and regularly readingthe current speed set point from the speed profile.

BACKGROUND ART

The automatic control of vehicles, particularly commercial vehicles suchas buses, has been studied with the objective of minimising emissionfrom vehicles and minimising energy consumption. In the article entitled“Control strategies for an electric Hybrid bus adapted to a specificroute”, by Jan Andersson, Roger Axelsson and Bengt Jacobsson, presentedat AVEC1998, the concept of “advisor” was introduced. This “advisor”,which constitutes a part of the control system of the vehicle,calculates a suitable speed profile on the basis of the planned route ofthe vehicle, i.e. the speed the vehicle should keep at each moment ofthe journey. The advisor regularly receives data as to the speed andposition of the vehicle and the current time, in order to update thespeed profile.

This speed profile shall then influence the driver with a view toachieving smoother driving and thus a more optimal energy consumptionand level of emission. In the article mentioned above the advisorinfluences the control system for the vehicle's engine directly. Theactions of the driver in depressing or releasing the accelerator andbrake pedals are regarded as input signals to the advisor, which thusacts as a kind of filter.

This entails a possible traffic danger for two reasons. In the firstplace the driver does not have sufficiently direct contact with thecontrol system of the vehicle. The advisor, which in a mathematicalmodel follows the behaviour of the driver, can hardly be prepared forall human behaviour. “Misunderstandings” may consequently arise betweendriver and advisor. In the second place there is a risk of the driverbeing lulled into playing an all too passive part since an advisorconstantly supervises his behaviour.

One problem with the use of such an advisor is to activate the driversufficiently so that his driving behaviour will be changed withoutcausing a traffic danger due to the driver becoming too passive.

OBJECTS OF THE INVENTION

The object of the present invention is to solve the above problem andprovide a method and a device for assisting a driver of a vehicle, suchas a bus, to promote a smoother style of driving with lower levels ofemission and lower fuel consumption.

Another object of the invention is to further develop the concept of an“advisor”, as mentioned above, and to implement this concept in avehicle.

SUMMARY OF THE INVENTION

To achieve the above objects the invention provides a method of the typedescribed above, characterised by the steps of controlling the engineand the braking system on the basis of the speed set point, by means ofat least one actuator influencing the accelerator or braking pedal ofthe vehicle in accordance with said control, determining whether thedriver is applying a force on one of the pedals that is greater than apredetermined threshold value and, if such is the case, allowing thedriver to override the influence of the actuator.

The method in accordance with the invention enables a vehicle to becontrolled in accordance with an optimal speed profile in order tominimise emission and fuel consumption. At the same time the driver isgiven information as to the signals transmitted to the engine andbraking system by the regulator. If the driver deems it necessary he canoverride the system, but only by applying sufficient force on thepedals. This force is determined to a suitable magnitude by means oftests depending, for instance, on the strength of the driver.

The force applied by the driver on a pedal may be determined by thepedal being movable against the action of a spring force, and a sensordetermining when the pedal has been moved a specific distance. The forceapplied by the driver on a pedal may also be determined by apiezoelectric element.

The information utilised by the method is in the first placed related tothe relevant distance to be driven, which is suitably divided intosegments, each segment being associated with a number of factors relatedto road conditions and speed limits, for instance, and to the time tableand planned stops along the route.

This information is entirely independent of the vehicle and may beincluded in a common information package tied to a specific route.

Secondly, the method utilises information related to the capabilities ofthe vehicle, such as engine power, transmission, inertia, etc. Thisinformation is similarly entirely independent of the route and may beincluded in an information package tied to a specific type of vehicle.

Thirdly, the method utilises continuous information from the internaldata system of the vehicle, such as speed, position and time. Thisinformation is already used in modern public transport vehicles and notechnical problems are entailed in obtaining it.

The step of controlling the engine and the braking system on the basisof the speed set point can be performed by direct activation of theaccelerator and the brake pedal. This gives a particularly clearcoupling between the control of the engine and braking system on the onehand, and the position of the pedals on the other hand.

In accordance with the invention a device is also provided forperforming the method.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in more detail in the followingwith reference to the accompanying drawings illustrating preferredembodiments of the invention by way of example.

FIG. 1 shows generally a control system for a vehicle provided with adevice in accordance with the invention.

FIG. 2 shows a flow chart for a part of the method in accordance withthe invention.

FIG. 3 shows a speed profile.

FIGS. 4 and 5 show the speed profile in FIG. 3, adjusted to comply witha time table.

FIG. 6 shows schematically how the pedal characteristic is changed witha device in accordance with the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT

The embodiment of the invention described in the following, which shallonly be looked upon as an example, relates to application in a bus withautomatic transmission that follows a route with several bus stopsaccording to a specific time table. The invention can naturally be usedto advantage in numerous other situations.

FIG. 1 shows schematically how the method and the device in accordancewith the invention are implemented. The engine and braking system of thebus I are controlled by one or more control systems 2 which areinfluenced by instructions from the driver 4 via the gas and brake pedal3. If the vehicle is of hybrid type the braking system comprises means,such as a generator, in order to take advantage of the braking energy.In accordance with the invention a device termed an advisor 5 is alsoarranged to influence the pedals via a regulator 6. The advisor 5comprises a database 7 containing data as described below, and means 8to determine the speed profile. The advisor also comprises a memory unit9. The regulator 6, consisting of substantially known hardware orsoftware, is arranged to convert signals from the advisor 5 todeflections of the pedals 3.

According to the invention, the task of the advisor is to determine howthe vehicle is to be driven from its current position to the next stop,e.g. a bus stop. A flow chart of how the advisor operates is shown inFIG. 2. The input data at each call are position, time and speed. Theresult of each call is a speed profile describing how the vehicle is tobe driven to the next planned stop. The speed profile comprises arelation between speed set point and position, which can of course beconverted by simple mathematics to a relation between speed and time.The routine illustrated in FIG. 2 is called regularly during the journeysince unforeseen events, such as red lights or sudden braking, maynecessitate adjustment of the speed profile.

The database 7 contains information concerning a division of therelevant route into several segments, each having a length of 10-100 m,for instance, and concerning a maximum suitable speed along eachsegment. A plurality of factors, such as speed limits, road quality,pedestrian crossings, intersections, etc. are taken into considerationwhen determining said maximum suitable speed along each segment.

The database 7 also contains information concerning factors associatedwith each segment that affect acceleration, such as incline and bends.The database 7 also contains information as to where planned stops, e.g.bus stops, are located on the route, as well as time-table information.

All this information, which is entirely independent of the vehicle, canpreferably be supplied from a central database (not shown) and beregularly updated. All vehicles travelling along the same route willtherefore have access to the same information and a vehicle that changesits route can be updated with new information. Updating of this type caneasily be accomplished using known technology, e.g. wirelesstransmission with suitable communication protocols.

The database 7 also contains information about a plurality of factorsspecific to a vehicle, such as weight, power transmission, inertia,engine power, etc. This information thus is the same regardless of theroute the vehicle is travelling at any particular time. Several factors,such as factors relating to the engine, are only updated in conjunctionwith service and maintenance, for instance, whereas other factors, suchas weight, can be affected during the course of driving by the number ofpassengers carried, for instance. The degree of detail in this lattertype of information is in principle limited only by the informationsystem of the vehicle.

The first step 10 denotes calling the routine, with the time, positionand speed parameters. These parameters are collected from the internalinformation system of the vehicle, which is suitably provided with someform of position-determining system, e.g. GPS. Information systems ofthis type are generally known and are becoming increasingly more usualin all types of vehicles.

In the next step 11 information is collected from the databaseconcerning suitable maximum speeds on the route in question.

On the basis of this information the first speed profile is determinedin step 12, this being defined by the vehicle following the highestsuitable speed along each segment of the road. This speed profile isillustrated by way of example in FIG. 3 for a distance to be driven.Since it is not possible to instantly alter the speed of the vehicle asindicated in FIG. 3, the program control in steps 13-15 performs anadjustment of the first speed profile to the factual accelerationsituation.

The previously mentioned acceleration-related factors associated witheach road segment are collected in step 13, and the vehicle-relatedfactors are collected in step 14 from the database. Calculation is thenperformed in step 15 to determine how the speed can be changed betweenthe various segments.

The algorithm in step 15 can utilise information about several segmentsahead, in order to coincide better with the original speed profile. Areduction in speed between two segments might, for instance, be followedby another, more substantial reduction in speed. In that case it may benecessary to entirely omit the intermediate speed level so as to enablebraking to the lowest level in time.

In step 16, therefore, a somewhat more uniform speed profile has beenobtained and the travel time to which this profile corresponds iscalculated and compared in step 17 with the time table, read from thedatabase 7. However, if the vehicle followed the first speed profile thetravel time would normally be far too short, and an algorithm istherefore usually required which reduces the speed in a systematicmanner, so that the stated travel time is maintained. After reduction instep 18 of one or more of the speed levels in the profile, steps 13-15are repeated, and the procedure is repeated until, in step 17, the timedriven coincides well with the time stated in the time table.

The speed reduction mentioned above can be achieved in many ways knownper se, and only two preferred methods will be presented here by way ofexample.

A first method involves multiplying the entire speed profile by ascaling factor, thereby reducing the maximum speed proportionally in allsegments. The scaling factor is determined by the iteration of steps13-15, which gives a speed profile that complies satisfactorily with thetime table. The result obtained by displacing the scaling factor andequalisation of the speed profile in FIG. 3 is shown in FIG. 4.

A second method involves introducing a new maximum permissible speed,and adapting the speed profile to this. In each segment that has amaximum suitable speed greater than the maximum permissible speedintroduced, the speed is reduced to the latter. The maximum permissiblespeed that satisfactorily complies with the time table is determined bythe iteration of steps 13-15. The result of such curtailment andequalisation of the speed profile in FIG. 3 is shown in FIG. 5.

After step 18 a speed profile has been determined that covers thedistance from the current position to the next stop and which ensuresthat the vehicle keeps as well as possible to the time table.

If something has occurred preventing arrival at the bus stop at theappointed time from the current position, this will immediately bedetected by the advisor at the first comparison in step 17. Examples ofsuch incidents are traffic congestion, unusually many red lights, orother disturbances in the traffic. The driver can be advised of theexpected delay and a message can also be sent to a traffic informationsystem.

The speed profile determined in this way is stored in the memory unit 7in step 19 and every time the speed profile is updated (after each callof the routine in FIG. 2), a new speed profile will be stored.

If the advisor is implemented in the form of software, or programmed ICcircuits, the routine in FIG. 2 can be performed in an instant. Callingthe routine relatively often, e.g. every second, thus constitutes noburden on the control system of the vehicle. The risk of sudden changesgiving rise to major changes in consecutive speed profiles is thereforeminimised. It can be said that the vehicle does not unnecessarily followan incorrect speed profile.

The regulator 6 continuously reads a current speed set point from thelatest speed profile stored in the memory unit 7 by the advisor 5 andcompares this with the factual speed of the vehicle which is fed back tothe regulator. The control system of the engine and the braking systemis then influenced in accordance with this difference. As regardsincreasing speed, the regulator functions in approximately the same wayas the equivalent software in a cruise control that regulates increasingspeed in accordance with a speed dictated by the driver. The regulatorfunctions in corresponding manner as regards braking, but with differentcontrol algorithms because of the different physical procedure.

In accordance with one embodiment of the invention, the speed set pointis converted to a set point for the position of the pedal and brakingforce, and is suitably in two steps. The first step generates a setpoint relating to acceleration (positive or negative) based on the speedset point in relation to the factual speed of the vehicle. Severaldifferent possible control strategies can be implemented by one skilledin the art. The acceleration set point is then converted to a set pointfor increasing speed or braking, depending on whether the accelerationset point is positive (acceleration) or negative (retardation). The setpoint relating to increasing speed, which shall control the accelerator,is expressed as a pedal position, and the set point relating toretardation, which shall control the brake pedal, is expressed as abraking force.

The regulator also controls actuators e.g. stepping motors (not shown),which directly influence the accelerator or brake pedal 3 of the vehiclein relation to the control of engine and braking system. It can be saidthat the actuators actuate the pedals to reflect the influence theregulator exerts on engine and braking system. If a vehicle equippedwith a device in accordance with the invention is not subjected toexternal influence, the pedals 3 will move as if an optimally driving“ghost driver” were manipulating them.

In accordance with one embodiment of the invention, the regulatorcontrols engine and braking system of the vehicle only by directlyactuating the accelerator and brake pedal. The effect of a “ghostdriver” is then even more palpable.

The driver is able to override the pedals controlled by the advisor byapplying foot pressure exceeding a predetermined threshold value on oneof the pedals 3. The driver is permitted to override the influence ofthe actuator only if a force greater than the predetermined thresholdvalue is applied on one of the pedals.

Each pedal may be provided with a spring means 20, for instance, whichforces the driver first to move the pedal a distance against the springaction before the movement will affect the control system (increasedspeed or retardation) of the vehicle.

In a simple example the spring means 20 consists of a helical spring orthe like, arranged between the foot-plate of the pedal and the vehicle'slink arm of the control system (see FIG. 6). A sensor (not shown) may bearranged to sense when the foot-plate has been moved a certain distanceand, if appropriate, emit a signal to disconnect the actuator, therebyreleasing the pedals entirely from influence of the advisor, or at leastreducing the force applied by the actuator.

Another possibility is to arrange a piezoelectric element on each pedal,which senses the pressure the driver applies on the pedal. When thepressure is sufficiently high the actuators are overridden as describedabove.

Also in accordance with the invention, a means can be arranged thatenables the driver to warn the advisor of imminent external influence,e.g. an obstacle on the road. This feature enables a form of “feedforward” of the control and gives the advisor the chance to take the newobstacle into consideration in the next call of the routine in FIG. 2.This “feed-forward” means may be more or less sophisticated and maypermit the driver to indicate an assessment of the distance to theobstacle, for instance.

It will be understood that the present invention shall not be limited tothe above description of preferred embodiments. Several modificationsobvious to one skilled in the art are feasible within the scope of theappended claims. A vehicle may be equipped, for instance, witharrangements for controlling increased speed and retardation other thanpedals. Furthermore, the factors mentioned for determining the speedprofile are only to be seen as examples. Several other factors may berelevant.

What is claimed is:
 1. A method for assisting a driver (4) of a vehicle(1), said vehicle having an engine and a braking system, an accelerator(3) that conveys the driver's wishes concerning acceleration to theengine, and a brake pedal that conveys the driver's wishes concerningretardation to the braking system, which method comprises taking intoconsideration several factors, such as a division of a specific drivingdistance into shorter segments, determining a speed profile (21 a, 21 b)for the driving distance, which speed profile comprises a relationbetween a speed set point and position, and regularly reading thecurrent speed set point from the speed profile, characterised by thesteps of controlling the engine and the braking system on the basis ofthe speed set point, by means of at least one actuator influencing theaccelerator or braking pedal of the vehicle in accordance with saidcontrol, determining whether the driver is applying a force on one ofthe pedals that is greater than a predetermined threshold value and, ifsuch is the case, allowing the driver to override the influence of theactuator.
 2. A method as claimed in claim 1, wherein the force thedriver applies on a pedal is determined by the pedal being moved aspecific distance against the action of a spring force.
 3. A method asclaimed in claim 1, wherein the force the driver applies on a pedal isdetermined by a piezo-electric element.
 4. A method as claimed in claim1, wherein the factors taken into consideration in the step ofdetermining a speed profile comprise traffic-related factors such asspeed limits and expected traffic congestion.
 5. A method as claimed inclaim 1, wherein the factors taken into consideration in the step ofdetermining a speed profile comprise acceleration-related factors suchas the incline of the road and bends in the road.
 6. A method as claimedin claim 1, wherein the step of controlling the engine and the brakingsystem on the basis of the speed set point is performed through directinfluenced on the accelerator and the brake pedal.
 7. A device forassisting a driver (4) of a vehicle (1), said vehicle having an engineand a braking system, an accelerator (3) that conveys the driver'swishes concerning acceleration to the engine, and a brake pedal thatconveys the driver's wishes concerning retardation to the brakingsystem, comprising means (5, 7, 8, 9) for determining a speed profile(21 a, 21 b) for a specific distance, which speed profile comprises arelation between a speed set point and position, characterised by means(6) for controlling the engine and the braking system on the basis ofthe speed set point, at least one actuator for influencing theaccelerator or braking pedal of the vehicle in accordance with saidcontrol, and means (20) for determining whether the driver is applying aforce on one of the pedals that is greater than a predeterminedthreshold value in order, if such is the case, to override the influenceof the actuator.
 8. A device as claimed in claim 7, wherein the meansfor determining a speed profile and for conversion of the speed setpoint are implemented in the form of software in the control system ofthe vehicle.
 9. A device as claimed in claim 7, wherein each pedal isarranged to be movable against spring action wherein a sensor isarranged to sense when one of the pedals is moved a certain distance.10. A devise as claimed in claim 7, wherein a piezoelectric element isarranged on each pedal to sense when a force of a certain magnitude isapplied on the pedal.
 11. A method for determining a speed profile for adriving distance that is divided into segments, which speed profilecomprises a relation between a speed set point and position,characterised by creating a first profile (step 12) by associating eachsegment with a maximum suitable speed level, smoothing outdiscontinuities arising between segments with different speeds (step15), calculating the time required to drive the driving distanceaccording to the profile determined (step 16), comparing this time witha predetermined time (step 17), if said calculated time is less thansaid predetermined time, reducing the speed levels in the profile (step18) until said times substantially coincide.